C++ :: How To Hold Pointers / References To Abstract Class
Nov 15, 2014
I have an abstract class named Terrain, and a class named RoadMap, which supposed to hold an N*N array of Terrains. But I'm not sure what type should the RoadMap class hold:
Code:
#ifndef TERRAIN_H
#define TERRAIN_H
class Terrain {
[Code] ....
I can't use an array of refernces here, so I tried this:
Code: Terrain** terrain; and then I thought this was the way to go:
Code: Terrain (*terrain)[]; But now I'm not sure.
The N*N matrix size supposed to be determined according to a given input... What type should I use there?
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May 13, 2014
I need to create a vector of pointers and hold the book objects in it. then i have a virtual function in my books which is a pure virtual in LibraryItems. When i try to add the books object in my code, i understand that since the scope runs out there is no object that is added. so when i run print it gives me an error.
#include<iostream>
#include "books.h"
#include "library.h"
#include <vector>
using namespace std;
int main(int argc, char * argv[]) {
vector<LibraryItems* >libraryInfo;
[Code] .....
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Feb 10, 2015
Using SFML, I had a Board class which held multiple vectors of all of my object types in the game, and then it also held a vector of pointers to the memory addresses of these object instances, like this
class Board{
//...
std::vector<AbstractObject*> GetAllLevelObjects(){ return allLevelObjects; }
//so these are used to hold my object instances for each level
[Code]....
When looping through this vector and drawing the sprites of the objects, I get the runtime error 0xC0000005: Access violation reading location 0x00277000. I solved this error by storing the vector of pointers in the class that holds my Board instance, but I'm wondering why only this solution worked? Why couldn't I just have my vector of pointers in the same class that the instances of those objects were in?
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Nov 12, 2014
This has been bothering me for a while now, and I finally put together an example:
#include <iostream>
#include <string>
using namespace::std;
[Code]....
In the code above, the two classes hold pointers to each other, and that's fine but it doesn't seem right since C++ prefers to pass by reference. Yes, it can still do that (see testbox and testball) but even that seems odd to me because still you need to use pointer notation for the enclosed object. Am I the only one who feels this way, and should I just get over it? Or am I missing something that would allow an object to hold a reference?
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Apr 8, 2013
Is there a point in dynamically creating a pointer during runtime only to dereference it? (if that is the right term, as in *pointer, depoint it?)
In this case should I perhaps store pointers instead of references?
Inventory.cpp
Code:
bool Inventory::addItem(InventoryItem& item) {
addItemAmount(item);
if (item.getAmount() > 0) {
if (hasEmptySlot()) {
addNewItem(*item.clone());
return true;
[Code] ....
Also I was wondering, is there some sort of built-in cloning functionality or do I have to write the clone functions myself? When creating new instances I see that I can either pass the constructor properties or a reference to an object of the same type.
For instance:
Code:
new InventoryItem(index, name....);
new InventoryItem(const InventoryItem&);
Is the second one casting?
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May 28, 2013
I have an abstract base class - let's call it MyInterface - and a class that most classes in my program inherit from, let's call it MyBaseclass.
Let's assume that all my objects inherit MyBaseclass, some of which also inherit MyInterface. Now I want to collect objects in a container class, MyContainerclass. The container class is only interested in objects that implement MyInterface.
Now I know that all objects that inherit MyInterface also inherit MyBaseclass, but the compiler doesn't know that. MyContainerclass wants to call methods in MyBaseclass, but it collects pointers to MyInterface classes. I can't make MyInterface inherit MyBaseclass, because I will be using classes that I don't want to change (they are part of a framework) that already inherit MyContainerclass. IOW, I can't use virtual inheritance to get a nice inheritance diamond.
To sum up, I want to create a container class that:
1. Collects objects that implement MyInterface.
2. Calls MyBaseclass methods on the collected objects.
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Dec 11, 2013
How would I use the list container to hold a class?
class A {
private : int x;
public : void setX(int val) { x = val; }
};
class B {
private : std::list<A> pdata;
public : void addToList();
};
For adding, I thought of trying something like
void B::addToList() {
A *tmp = new A;
if(A != 0) {
tmp->setX(5);
pdata.insert(tmp);
delete tmp;
}
}
How would I do what I'm trying to do? Or is this the wrong way to go about it? For the actual program, "B" would contain several lists of various classes.
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Dec 28, 2012
two more questions
Code:
#ifndef PERFECTSIM_PARSER
#define PERFECTSIM_PARSER
#include <string>
#include <d3dx9.h>
#include <sstream>
#include <iostream>
#include "tinyxml inyxml.h"
using namespace std;
template<class T>
class GetValue {
protected:
virtual T get(TiXmlNode* pParent);
[code].....
1) Can't instantiate abstract class of GetVector3.
2) Don't you think the coding is very redundant ?
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Feb 17, 2013
I have this header file called Shape.h containing these function declarations. and a Shape.cpp which contains the body of the function. I am not showing it since it is not needed.
//This is from Shapes.h header file
#ifndef SHAPES_H
#define SHAPES_H
#include <iostream>
[Code]....
I have this unfinished Main.cpp because the third line "JuanSanchez::Circle *pCar = new Circle; " is giving me a compiler error "error C2061: syntax error : identifier 'Circle' "
#include "Shapes.h"
int main()
{
const int arrayIndex = 4;
JuanSanchez::Shape *myShape[arrayIndex];
JuanSanchez::Circle *pCar = new Circle;
}
What Could be causing this error?
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Nov 11, 2014
I have the following code:
class Element {
public:
..
virtual unsigned NumberOfNodes() = 0;
[Code] ....
Is it possible to implement this better? All the element stuff can be static, but this is not possible with the abstract class. I want to have Mesh independent of a specific element. With the code above, if I have multiple meshes I have one instance of an element, e.g., Triangle for each mesh. Although they are all exactly the same.
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Oct 13, 2013
I am working on a project that requires me to create objects from a abstract class that has 2 child classes (that need to be derived). Any examples on how to do this? I looked online and the examples were pretty vague. the main error that I am getting is when I make a temp object with & in front of it (such as Employee &genericEmp) it throws a must be initialized error.
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Oct 3, 2014
I want to create an abstract base class having a member function that can accept a templatized structure as its parameter, something that according to C++'s rules can't be done for a good reason.
That good reason it is because an abstract base class is intended to provide interface rules to the classes that will derive from it and should not deal with data.
But how would you go about doing something like the following which is probably a reasonable design decision?
template<typename T>
class Matrix { /* ... */ };
class iFile {
public:
virtual ~iFile() {} = 0;
virtual void Process(const Matrix<T>&) = 0;
[Code] .....
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Feb 14, 2013
I am making a snake game just to give some context.
//LevelObject.hpp
class LevelObject {
public:
virtual void Update() = 0;
virtual void Draw(Canvas& canvas) = 0;
protected:
Vector3 location_;
[Code] ....
The problem I have is with the Size constructor and the abstract class LevelObject which size is a member of.
The compiler error I get is:
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
[Code] .....
However I do invoke the copy constructor when I pass a variable of type size to the constructor in this line:
size_ = Size(s);
But the problem is that its complaining that the abstract class LevelObject doesn't invoke the constructor, which it shouldn't.
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Apr 3, 2014
I was wondering if there is way to convert a C# class to its own project and it automatically keeps its references.
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Jun 22, 2012
I have an abstract class called Mbase and from it derived two classes: Sparse and Dense. Now I have an array in which its elements can be either Sparse or Dense. So, I delcared the array to have pointers to Mbase class. For example:
PHP Code:
Mbase** A;
Sparse* A1 = new Sparse;
Dense* A2 = new Dense;
A[1] = dynamic_cast<Mbase*>(A1);
A[2] = dynamic_cast<Mbase*>(A2);
Now, I have operator + defined in Sparse and Dense. but when I do
PHP Code:
A[1]+A[2]
I get that operator + is not defined for Mbase class. So, I tried to define it in the Mbase class
PHP Code:
class Mbase{
public:
void put()=0;
double get()=0;
Mbase operator +(Mbase A);
}
However, the last code does not compile complaining that it cannot declare a class of type abstract in Mbase operator +(Mbase A). I think this is because I am returning Mbase instance.
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Jul 27, 2012
As i have one Abstract base class say MyBase.
It have parameterized constructor with string value it have abstract method call.And I also have One child class say MyChild.
It does not have any constructor only one have public method and i want to call that parameterized constructor of base class onto child class.
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Oct 2, 2013
Imagine if there is an abstract class with a method (say output or print) which would be inherited by a few other classes. Later objects are created using the inherited classes, and the user wishes to call the above method twice, for eg (i) output/print to screen and (ii) output/print to a file. What is the best way to achieve that.
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Jun 19, 2014
I am working with a new text adventure. The way i want to construct it is by having a class for all living things. in the class you have basic things as: health, gold, vector for inventory holding "struct item". etc...
There is also a class called world, wich navigates through the world.
World class contains of: player location, and a map containing info about the room etc...
Here comes the problem. I want there to be characters to be placed out in different maps, so basically i want the world class to hold objects from Character.
How to do it. In world class i made a map...
std::map<int,"content">
content is a struct i made above in world class:
struct content{
std::string name; // location name
std::string info; // info about location
std::vector<Character>characters;
std::vector<item>items;
};
To sum it up, i have a std::map<int,content>map the int stands for location id. Content holds more info about the room and what's in it
btw the classes are in different files and that means i have to include "Character.h" in the world file so i can set up the vector of characters.
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Feb 27, 2014
I'm trying to implement a decision tree that gets doubles as input (in this sample code just random numbers) and returns a boolean value. At the nodes, I'd like to use various operators that can have different input and return types. I've implemented an abstract base class for the nodes and I'm deriving the specific nodes from it. In the code below, I've included only a few derived classes. Building the tree (randomly) is no problem. However, I'm looking for a clever way to evaluate the tree. I think that uncommenting the lines in bold print would in principle do it. However, this is not possible because "value" is not a member of the base class. The type of "value" is different in the derived classes, so I cannot simply declare it in the base class.
"Node.h"
#pragma once
class NodeBase{
public:
NodeBase* Child_1;
NodeBase* Child_2;
virtual void evaluate() = 0;
[Code] ....
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Dec 3, 2014
A have two classes, one inheriting the other, and the parent class being abstract (I plan on adding more child classes in the future). For reasons I won't bother mentioning, I'm making use of an STL container as a way for me to access all of the child objects in the heap. I've done so by making use of a map, with key type int and value type being a pointer to the parent class:
//PARENT.H
class Parent {
protected:
static int n;
static std::map<int, Parent*> map;
public:
virtual void pureVirtual() = 0;
[code]....
The Problem:In line 5 of Parent.cpp, initializing the value of the element to new Child won't work, as according to the compiler, the Child class hasn't been declared yet, and including Child.h into the Parent.h only opens an even bigger can of worms.I also can't initialize it as new Parent, seeing as the parent class is an abstract one.
The Question:Is there a way I can initialize the static map properly. Making the Parent class abstract is not an option.
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Jul 11, 2012
For example, in a header file A.h, I define an abstract class,
Code:
// A.h
class A {
public:
virtual void foo() = 0;
private:
static int _x;
};
How'd I initialize static member data _x?Normally, we initialize a static member data in a cpp file. However, there is not cpp file for A.h. If I intialize _x in header file, there will be linker errors like mulitple defined symbols. What is appropriate way to do that?
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Mar 6, 2014
The abstract class can provide more functionality without affecting child classes.If we add any method to the interface ,then will it affect all the child classes ?
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Jan 16, 2013
Please consider the following code :
#include <iostream>
using namespace std;
class superclass;
class subclass1;
class subclass2;
[Code] ....
As you can see I want to create a dynamically allocated storage of references to a parent class each of which can then point to a child class, how ever I do not know how to extract the child class out again from that array so i may access its variable b.
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Nov 19, 2013
I wrote a class to manage pointers better (because I am making a large program and don't want to call a constructor on somthing that was already deleted... etc...), but I am getting some compiler errors. I'm not sure what to do.
here is the class prototype:
template<typename type>
class pointer_class{
public:
pointer_class() : dat(NULL), del(false) {}
explicit pointer_class(const pointer_class<type>& d) : dat(NULL),
[Code].....
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Apr 25, 2014
Class with Pointers and Dynamic Arrays
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Jun 8, 2014
How can i use a function pointer from external class? Say we have a class tuna
Tuna:
int foo(){
return 45;
}
int (*foobar)();
[Code].....
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